Influence of pressure on dislocation, disclination, and generalized-disclination structures of a {310}/[001] tilt grain
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nt Taupin Laboratoire d’Etude des Microstructures et de Mécanique des Matériaux (LEM3), Université de Lorraine/CNRS, Ile du Saulcy, 57045 Metz Cedex, France
Patrick Cordier Unité Matériaux et Transformations, UMR 8207 CNRS/Université Lille1, Villeneuve d’Ascq, France
Claude Fressengeas Laboratoire d’Etude des Microstructures et de Mécanique des Matériaux (LEM3), Université de Lorraine/CNRS, Ile du Saulcy, 57045 Metz Cedex, France
Bijaya B. Karki School of Electrical Engineering and Computer Science, Louisiana State University, Baton Rouge, Louisiana 70803, USA; and Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803, USA (Received 5 June 2016; accepted 7 September 2016)
Due to gravitational self-compression, the pressure in planetary interiors can reach millions of times the atmospheric pressure. Such high pressure has a significant influence on their rheology. In the present paper, we focus on how pressure in the range of the Earth’s lower mantle may influence the structure of a MgO {310}/[001] tilt boundary. The defected structure of the grain boundary (GB) will be described through its dislocation, disclination, and generalized-disclination (g-disclination) density fields. At first, the strain and rotation fields in the boundary area at different pressures are derived from the discrete atomic positions simulated by first-principles calculations. For each pressure, the discontinuities of displacement, rotation, and strain in the boundary area are continuously rendered by dislocation, disclination, and g-disclination density fields, respectively. These density fields measured at different pressures are compared to provide understanding on how pressure does influence the GB structures in Earth materials.
I. INTRODUCTION
In the Earth’s mantle, with increasing depth, pressure increases rapidly, reaching values as high as 136 GPa at the base of the mantle.1 These ultrahigh pressures have profound implications on the rheology of the Earth’s constituents that can be quite different from that observed at ordinary pressure. Therefore, it is of primary importance to investigate the mechanical behavior of the highpressure phases of the deep Earth to understand the structure and dynamics of the Earth’s interior. Below 670 km, the phase assemblages present in the Earth’s transition zone decompose into a mixture of silicates with the perovskite structure and magnesium oxides (containing some iron). The high-pressure behavior of periclase (MgO) is thus of major importance in the Contributing Editor: Susan B. Sinnott a) Address all correspondence to this author. e-mail: [email protected] This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2016.346
rheology of the Earth’s interior. MgO is an ionic solid, which is chemically and physically stable at high temperatures and pressures. It can keep its NaCl-type structure up to 227 GPa confining pressure.2 This unique structural stability makes MgO an ideal benchmark for investigating the behavior of solids at extreme
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